Gas gauge issue

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erndog72

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For many months my 2004 Montana (extended) has had a fuel gauge problem. The gauge always indicates either completely full or completely empty. Never anything in-between. It also has nothing to do with actual level in the tank; it doesn't care. Since I also had ABS issues, I suspected connector C305 and replaced it, even though it looked good to me, since both ABS and fuel system wiring go through it. That did nothing for either one and eventually I fixed the ABS by replacing the EBCM. I was/am getting a P0463 DTC [FUEL LEVEL SENSOR A HIGH INPUT], so all things considered it seemed to be the sending unit. Well, I dropped the tank and replaced the sending unit this morning with GM part# SK1127. The wipers on the old unit were half gone. I got it all back together and voila! ...same old problem. The gauge pegged out high for a few seconds and then failed low. Thinking it was just re-zeroing I filled the tank half-way. The gauge registered completely full. I then proceeded to put in the remaining 14 gallons. Still pegs high or low.

Could it be the PCM? Any ideas out there??

PS. I ran a check on the crappy old sending unit after the fact and it is in working condition.

:confused::confused::confused:
 
Hi !
Fuel gage likely completes circuit thru the ground . For this reason one of the first things to check is the wiring and for proper grounding of the sending unit . A loose wire on the level transmitter circuit could be the reason . Search for a bad wire.

 
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Thanks. Yeah, I thought about that, too. I didn't see anything obvious when the tank was off, but like an idiot, I didn't do a continuity check while I had the chance. If there is a wire issue, it must be from c305 forward. Not an easy thing to look for.
 
I did a similar replacement earlier this year. While doing it, I also removed the board that the wipers sweep across. I then hooked everything up and noticed that my near-empty tank was registering near full. It also went empty when I filled it. I removed the mess again, and looked at the two boards and found that they were wired in reverse, so that it would give higher ohms readings when it was empty. It should be 40 ohms empty and 250 ohms full, but mine was backwards. It'd be worth testing the sender to see what your ohms are across it. Then you can chase down your possible ground fault.
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The sender is a brand new factory original replacement, with factory wiring. That's not the issue. Plus, with a full tank it is still reading max full or max empty, depending on its mood.
Good thought, though.
 
Don't know what happened but I just jumpered c305 3B and 3D to see if everything worked from there forward and it did. Jumpered made gauge read empty and open made it read full. Then I tested across the points going back to the sender and got 0 ohms on a full tank. That tells me there is an issue back there or in the wiring harness. HOWEVER, now the engine won't start. At all. It cranks beautifully, but either the pump isn't running or the spark is gone. ?????????????
 
Back in the day on my 2000 Montana I had a bad connection on the connector block from the pump assembly . Some where near the top of the tank, it was burned up and real hard to tell .
 
I have verified I am getting spark. Evidently I am not getting fuel for some reason. I tried replacing the fuel pump relay, but that doesn't help.
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Is the fuel pump getting power when ur cranking? When u turn the key can u hear the pump pressure up then shut off? Also have u checked the pressure at the fuel rail when cranking?
 
I crawled under the van tonight after I got home from work. I unplugged the tank harness from C305 to verify I didn't break a stab off or something, or only partially reconnect the plug. Everything looked good. However, the gas tank harness plug (female part) appeared to have some connectors that may have been spread a bit too much. After a minute or so I realized there wasn't much I could do about them. So I put just a little spreading pressure on the matching stabs and firmly reseated the connection. Guess what? The van started right up! Damn, am I relieved. Needless to say, I just ordered a factory original replacement harness. Thanks to everyone for their advice! I will post if this fixes the tank level indication as well.
:) :) :)
 
Hi !
I think that this problem in the connector C305, where the harness goes into the body. They are subject to weather conditions and seem to have some problems


... or ground (ground G301 located in the mid pillar of the van)
 
If you read the opening post, you will see that I already replaced C305. However, G301 is definitely a possibility. Thanks.
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I installed the new wiring harness tonight. It goes from C305 on back. I put the remaining 3 gallons of gas back into the tank and then filled it with 10 more gallons. The gauge went from just above empty to approximately half full and stayed there for the whole drive home.
VOILA! Case closed.
 
So Erndog, did you have to drop the tank to replace the whole wiring harness? I have the same problem, the guage always reads full.
 
Yes. It really wasn't that big of a deal. Worse thinking about it than doing it. Just drive it until it has used up most of the gas and then go at it. Be sure it is nearly empty or empty, though. The tank is very long and made of plastic, so you don't want to put too much stress on it. I used a floor jack under it with a board to spread out the load on. Of course, you need to put the car on jack stands to give adequate clearance when you drop the tank. You may want to go ahead and replace the sending unit while you have it apart. The one I got was factory original and a very reasonable price.
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